Self-encoding key switch and keyboard system utilizing the same

ABSTRACT

A self-encoding key switch is formed of a body having a well at the bottom thereof for storing a pool of mercury, a contact chamber for receiving the mercury from the well and a relief chamber for receiving the mercury from the contact chamber, and a plunger movable into the well to displace the mercury into the contact chamber to electrically connect a supply contact and a plurality of encoding contacts disposed in the contact chamber. The configurations of the body and the plunger cooperate to provide a path for the mercury to flow from the contact chamber to the relief chamber after momentary electrical connection of the supply and encoding contacts thereby providing N-key rollover. A keyboard system utilizes a plurality of the abovedescribed self-encoding key switches along with a register, and a strobe contact is disposed in the contact chamber of each key switch such that, after electrical connection is established between the supply and encoding contacts, the strobe contact is connected to trigger the register and enter the encoded data from the encoding contacts.

United States Patent 1 Faustini 1 SELF-ENCODING KEY SWITCH AND KEYBOARD SYSTEM UTILIZING THE SAME [76] Inventor: Carlo Faustini, 13020 Tamarack Rd., Silver Spring, Md. 20904 [22] Filed: Feb. 11, 1974 [21] Appl. No.: 441,496

[52] US. Cl 200/209; 200/214; 340/365 E [51] Int. Cl. I-I0lh 29/18; G08c 9/00 [58] Field of Search 200/1 R, 5 R, 5 A, 159 R, 200/159 B, 187, 188, 189, 2092l9;

307/106; 235/145 R; 340/365 R, 365 A,

OTHER PUBLICATIONS RCA Technical Notes, Carl A. Eggert, Mercury Operated Keyboard, Sept. 25, 1968; TN No.1773; pp. 1 and 2.

[ Sept. 2, 1975 Primary Iiruminer.lames Rv Scott Attorney, Agent, or FirmRobert-H. Epstein ABSTRACT A self-encoding key switch is formed of a body having a well at the bottom thereof for storing a pool of mercury, a contact chamber for receiving the mercury from the well and a relief chamber for receiving the mercury from the contact chamber, and a plunger movable into the well to displace the mercury into the contact chamber to electrically connect a supply contact and a plurality of encoding contacts disposed in the contact chamber. The configurations of the body and the plunger cooperate to provide a path for the mercury to flow from the contact chamber to the relief chamber after momentary electrical connection of the supply and encoding contacts thereby providing N-key rollover. A keyboard system utilizes a plurality of the above-described self-encoding key switches along with a register, and a strobe contact is disposed in the contact chamber of each key switch such that, after electrical connection is established between the supply and encoding contacts, the strobe contact is connected to trigger the register and enter the encoded data from the encoding contacts.

28 Claims, 17 Drawing Figures P NT WP 59. 5 0 9,

sum 1 OF 4 PATENTEBSEF m5 SHEET u 0 4 FIG.

BACKGROUND OF THE INVENTION 1. Field of the invention The present invention pertains to electrical key switches and, more particularly, to self-encoding key switches for use with data-entry keyboard systems.

2. Description of the prior art Due to the rapid growth of the computer, information handling and data processing industries the demand for low, cost, reliable keyboards and keyboard systems for data-entry is increasing since keyboards provide a natural and convenient interface between human operators and the electronic equipment. To this end, keyboards are familiar input devices for computers and peripheral equipment thereof, calculators, display devices and general communication terminals.

The heart of a keyboardis the individual key switches which are actuated by an operator to generate corresponding coded electrical signals. Key switches for use with keyboards can generally be classified in two major categories; that is, contact and non-contact switches. In contact key switches, a physical contact must be established, such as in reed, cross bar, elastomeric, mercury filled tube, magnetic repulsion and coil spring, crosspoint switches to name a few. Non-contact switches do not require such physical contact and include Halleffect, capacitive-coupled, saturating magnetic core and photoelectric switches, to .name a few. Most contact key switches produce only a simple make or break signal, such as a, contact closure, to provide an output voltage or a change of value of someelectrical parameter (resistance, capacitance or i nduct a"n'ce); and, for this reason, keyboards utilizing such key switches require, in addition to the appropriate number of key switches, electronic circuitry for converting r encoding the key switch signals into desired acceptable codes, for matching the interface characteristics of the associated electronic equipment and for providing Nkey rollover to overcome the problem of erroneous signal transmission caused duringburst speed key depression when previously striigk keys remain depressed while additional keys are depressed. Some nori-contact key switches have overcome some of the disadvantages of contact key switches; however, such non-contact key switches have the disadvantages of being relatively expensive and requiring standby power.

Accordingly, it is desirable for key switches to provide the features of N'key rollover and self-encoding; and, further, it is desirable for key switches to provide tactile feedback to the operator in that such tactile feedback essentially duplicates the feel of electric typewriters due to the key force increasing with key displacement until the moment of switch closure whereat the force of pressure drops suddenly. Another desirable feature in key switches is the strobe function which op erates to signal the associated electronic equipment that an encoded output has been obtained.

Since key switches and the electronic circuitry for use therewith represent a substantial portion of the cost of keyboards and keyboard systems, many attempts have been made to reduce the electronic circuitry re quirements as well as to reduce the cost of the key switches. These attempts in the prior art have not been successful in that attempts to provide self-encoding key switches to reduce circuitry costs have utilized noncontact type switches and, therefore, have increased switch costs while attempts to reduce the cost of key switches have required electronic encoding circuitry and, frequently, additional circuitry to match one type of interface circuit with another thereby increasing electronic circuitry costs. Attempts to develop low cost, self-encoding key switches utilizing a plurality of mechanical contacts have suffered the disadvantages of contact bounce and the inability to economically provide long life, high reliability and Nekey roll over.

SUMMARY or THEQQINYENTION The present invention is generally summarized in an electrical key switch including a body having a well for storing a pool of electrically conductive liquid, a contact chamber for receiving the liquid from the well, and a relief chamber for receiving the liquid from the contact chamber; electrical contacts mounted in the body and extending into the contact chamber; a plunger movable into the well to displace the liquid into the contact chamber; and means for providing a path for the liquid from the contact chamber to the relief chamber whereby the liquid remains in the contact chamber only momentarily.

Accordingly, it is a primary object of the present in-' a plurality of contacts therein such that a pool of mercury or other electrically conductive liquid can be dis placed into the contact chamber tofprovide only.momentary connection between the contacts thereby providing Nkey rollover.

The present invention has a further object in thecoh struction of an inexpensive, self-encoding key switchformed of plastic components and utilizing a pool of mercury displaceable by a plunger to provide momentary connection between a supply contact and a plurality of encoding contacts. V

Yet another object of the present invention is to form a key switch of a body having a well formed in the bot-i torn thereof with a contact chamber anda' relief char'n ber communicating therewith and defined by upstanding sidewalls extending substantially transversely rela tive to the bottom of the body such that movement of a plunger displaces mercury in the well into the contact chamber and thereafter the mercury collapses into the relief chamber to provide momentary electrical connection between contacts in the contact chamber.

The present invention has an additional object in that a contact chamber in a body of a self-encoding key switch has a plurality of encoding contacts disposed therein, a supply contact disposed in the contact chamber spaced from the encoding contacts and a strobe contact disposed in the contact chamber above at least a portion of the encoding contacts such that an electrically conductive fluid forced into the contact chamber will connect the supply contact with the strobe contact after connection has been established with the encoding contacts, the strobe contact being adapted to be A further object of the present invention is to provide a data-entry keyboard system formed of a plurality of self-encoding key switches each having contacts therein adapted to be momentarily connected by an electrically conductive liquid, and a register having data inputs connected with selected ones of the encoding contacts of each key switch and a strobe input connected to the strobe contact of each key switch such that actuation of any of the key switches enters coded data directly into the register.

Yet an additional object of the present invention is to provide a plunger and a body of a key switch with configurations such that a pool of mercury is forced in a piston-like manner into a contact chamber and thereafter the pool of mercury collapses to flow out of the contact chamber and/or is forced through the contact chamber into a relief chamber thereby providing tactile feedback and N-key rollover.

The present invention has a further object in that a self-encoding key switch has a plurality of encoding contacts and a strobe contact arranged in a contact chamber relative to each other such that the leading edges of data signals from the encoding contacts are generated before the leading edge of a strobe signal from the strobe contact and the trailing edges of the data signals are generated after the trailing edge of the strobe signal to permit the key switch to be used with both leading edge and trailing edge responsive circuitry.

Some of the advantages of the present invention over the prior art are that the key switch of the present invention can be simply and inexpensively produced while providing tactile feedback, self-encoding and N-key rollover features, and a keyboard system utilizing key switches according to the present invention can be inexpensively produced due to the lack of a require ment for electronic circuitry for encoding and matching with various interfaces.

Other objects and advantages of the present inven tion will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a broken exploded view of a key switch according to the present invention.

FIG. 2 is a vertical section of the key switch of FIG.

FIG. 3 is a section taken along line 33 of FIG. 2. FIG. 4A, 4B, 4C, 4D and 4E are vertical sections illustrating the operation of the key switch of FIG. 1.

FIG. 5 is a broken perspective of a portion of a key board utilizing key switches according to the present invention.

FIG. 6 is a schematic diagram of a keyboard system utilizing key switches according to the present invention.

FIG. 7 is a broken exploded view of a modification of the key switch of the present invention.

FIG. 8 is a vertical section of the key switch of FIG. 7.

FIG. 9 is a section taken along line 9-9 of FIG? 8.

FIGS. 10A, 10B, 10C and 10D are vertical sections, illustrating the operation of the key switch of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT A key switch 10 according to the present invention is illustrated in FIGS. 1, 2 and 3 and includes a body 12 made of a plastic material and'having a generally cylindrical outer side wall 14 closed at its bottom by a base 16. The body 12 has a top wall 18 made of a plastic material and secured to the upper edge of side wall 14, such as by ultrasonic welding or any other suitable means, and the top wall 18 has an opening 20 therein leading to a piston chamber 22 defined by an arcuate inner wall 24 concentric with side wall 14 and terminating at an end 26 spaced from the base 16. An arcuate relief chamber 28 is formed in the body 12 communicating with the piston chamber 22 and is defined by side wall 14 terminating at a sloping shoulder 30 disposed above the base 16 at a level even with. the end 26 of the inner wall 24. An arcuate contact chamber 32 is defined between outer wall 14 and inner wall 24 opposite the relief chamber-28 and communicates via an opening defined by the end 26 of inner wall 24 with a well 34 for receiving a pool of electrically conductive liquid 36, such as mercury, as shown in FIG. 4A. The well 34 is formed in the bottom of the body 12 and defined by base 16 and an upstanding end wall 38 having an arcuate segment terminating at shoulder 30 such that the relief chamber 28 and the contact chamber 32 communicate with the well 34 and are vertically displaced thereabove.

The inner wall 24 has longitudinal grooves 40 disposed on opposite concave sides thereof, and the piston chamber defined by inner wall 24 has a diameter substantially the same as the diameter of a piston-like head 42 carried by a plunger 44 made of a plastic material. The plunger 44 has an elongate shaft 46 with a key top 48 secured to a top end thereof, and the plunger 44 has a reduced diameter stem 50 extending from the bottom of shaft 46 to mount the head 42 which has a frustoconical upper surface. A pair of nibs 52 extend transversely from the longitudinal axis of the shaft 46 on opposite sides thereof; and, similarly, a pair of tongues 54 extend from opposite sides of the shaft 46 at the end thereof adjacent the stem 50. The opening 20 in the top wall 18 of the body 12 has an annular groove 56 formed therein, and an O-ring seal 58 is disposed in the groove 56 to provide a fluid-tight seal with the shaft 46 of the plunger 44, the plunger being slidably disposed in the piston chamber 22 with the tongues 54 riding in the grooves 40 to prevent rotation of the plunger and the plunger being biased away from the body 12 by a coiled return spring 59 mounted in compression between the outer surface of top wall 18 and the nibs 52.

A common or supply wire contact 60 is mounted in the outer wall 14 of the body 12 such that a contact end 62 thereof'extends into the contact chamber 32 and a connection end 64 of the supply wire 60 extends through the outer wall 14 of the body. The supply contact 60 has its contact end 62 disposed near the bottom of the contact chamber 32 to initially contact the mercury 36. A plurality of encoding wire contacts 66 are mounted in the outer wall 14 and have contact ends 68 grouped at substantially the same level extending into the contact chamber 32 above the contact'end 62 of supply contact 60 while connection ends 70 of the encoding contacts extend through the outer wall 14 of the body. A strobe wire contact 72 is also mounted in the outer wall 14 of the body and has a contact end 74 extending into the contact chamber 32 at a position above the contact ends 68 of encoding contacts 66 while a connection end 76 of the strobe contact extends through outer wall 14 of the body.

The operation of the key switch will be described with respect to FIGS. 4A-4E wherein it can be seen that initially the pool of mercury 36 is disposed in the body 12 to be received in the well 34 with the top level of the mercury being about level with the end 26 of inner wall 24, as shown in FIG. 4A. The pool of mercury 36 initially rests in the well 34 such that'the only possible contact made thereby is with supply contact 60. The head 42 of the plunger 44 is biased out 'of the well 34 by the return spring 59 such that the piston-like head 42 is spaced from the pool of mercury 36.

When the key switch is actuated by pressure on key top 48, the plunger 44 is axially moved into the body 12 in substantial sealing engagement with inner wall 24 and end wall 38 of the well 34 such that the pool of mercury 36 cannot exit the well into the relief chamber 28 but must flow through the opening defined by the end 26 of the inner wall and into the contact chamber 32. As shown in FIG. 4B, the mercury will be displaced by the movement of the plunger 44 to be forced into contact chamber 32 and establish electrical connection between the the supply contact 60 and the encoding contacts 66 and the strobe contact 72. Since the strobe contact 72 is disposed above the encoding contacts, once the electrical connection is made with the strobe contact all of the encoding contacts will have been previously connected with the supply contact 60; and, therefore, the leading edge of the strobe signal from the strobe contact will be generated after the leading edges of the data signals from the encoding contacts.

Once the plunger 44 has been depressed a predetermined distance such that the upper surface of head 42 clears the end 26 of inner wall 24, the column of mercury in the contact chamber 32 will collapse and flow through the path formed in the plunger by the reduced diameter stem 50 as shown in FIG. 4C to be received at least partially in the relief chamber 28. In this man ner, the electrical connections provided by the mercury in the contact chamber 32 are only momentary; and, even if the plunger is maintained in its depressed state, only a single coded electrical signal will be provided by the key switch. As the mercury in the contact chamber 32 collapses, strobe contact 72 is disconnected from the supply contact 60 before disconnection of the encoding contacts 66; and, thus, the trailing edges of the data signals will be generated after the trailing edge of the strobe signal. Accordingly, the strobe signal can be utilized to enter the coded data signals into suitable electronic equipment regardless of whether the electronic equipment operates on leading or trailing edges of signals. The movement of the plunger 44 required to permit collapse of the mercury in the contact chamber can be such as to move the head 42 into abutment with the base 16 of the body or any predetermined distance such that the head 42 clears the end 26 of the wall 24 to provide a flow passage for the mercury. Thus, the relative configurations of the plunger and the body structure defining the contact chamber should be such as to permit flow from the contact chamber after movement of the plunger 44 a predetermined distance, pref erably by the axial length of head 42 being less than the axial length of the opening formed atthe end 26 of the inner wall 24. Since the contact chamber 32 is sealed at its upper end by top wall 18, air will be compressed by the movement of mercury into the contact chamber, and the compressed air plus the flow of the mercury due to the force of gravity will provide tactile feedback to the operator once the plunger has been moved the predetermined distance.

Once the operator has moved the plunger 44 the predetermined distance, as can be determined from the tactile feedback, the key top is released, and the return spring 59 will move the plunger on its return stroke out of the well 34. Initial movement of the plunger upward is illustrated in FIG. 4D; and, once the head 42 of the plunger clears the juncture of end wall 38 and shoulder 30, the mercury will fall back into the well 34 aided by the sloping contours of shoulder 30 and the upper surface of the head 42, as shown in FIG. 4E. Thereafter, the key switch will be returned to its initial state, as illustrated in FIG. 4A, in preparation for the next depression of the plunger.

A portion of a keyboard utilizing the key switches 10 according to the present invention is illustrated in FIG. 5 wherein the key switches 10 are mounted on a suitable base 78 with the key tops 48 extending therethrough to be accessible for actuation by an operator, the base 78 being mounted in a substantially horizontal position and each of the key tops 48 being provided with indicia corresponding to data to be entered into electronic equipment.

A keyboard system according to the present invention is illustrated schematically in FIG. 6 wherein only three key switches 80, 82 and 84 are illustrated, each of the key switches having the structure described above with respect to key switch 10. The supply contact 60 of each of the key switches 80, 82 and 84 is connected to a supply potential, such as ground or any other positive or negative reference potential, by means of a common bus connector 86. A storage register 88 includes a plurality of data inputs A, B, C, D, E and F for receiving coded data from the key switches and a strobe input S for entering data on the data inputs into the storage register. The storage register 88 will normally be part of the electronic equipment with which the keyboard is to be used and is connected with the keyboard via a suitable interface 89. The strobe input S of the storage register is connected with the strobe contact 72 of each of the key switches 80, 82 and 84 by a connector 90 while the data inputs A, B, C, D, E and F of the storage register receive data from connectors 92, 94, 96, 98, and 102, respectively. Preselected ones of the encoding contacts 66 of each of the key switches are connected to desired connectors 92, 94, 96, 98, 100 and 102 in accordance with the code to be utilized by the keyboard and the data to be entered in the storage register in accordance with actuation of each key switch, and those encoding contacts not required for the coded data from each key switch can be left unconnected or can be connected to an adjacent encoding contact. Each of the data and strobe inputs is connected through a suitable resistor to a positive voltage source Vcc such that each of the inputs to the storage register has a positive potential thereon when no key switch is depressed.

In operation, each time a key switch is actuated, the supply contact 60 will be connected with all of the encoding contacts 66 thereof to place the supply potential on selective ones of the connectors 92, 94, 96, 98, 100 and/or 102 for input to the storage register 88. For example, when key switch is actuated, the ground potential from connector 86 will be supplied to connectors 92, 98, 100 and 102; and, thus, data inputs A, D, E and F of the storage register will be at ground potential or low input while the remaining data inputs B and C will be at Vcc or high input. Once ground potential is supplied to the strobe contact 72, which occurs after ground potential is established at the encoding contacts, a strobe signal will be supplied via connector and strobe input S to trigger the storage register 88 and enter the coded data signals from the encoding contacts 66 of the actuated key switch, the register 88 being responsive to either the leading edge or the trailing edge of the strobe signal since the strobe signal commences after the data signals and ends before the data signals. In similar fashion, when key switch 82 is 'actuated, data inputs C, D and E will be low, and data inputs A, B, and C will be low when key switch 84 is actuated.

Since the mercury 36 in contact chamber 32 co]- lapses as soon as the plunger 44 has been moved a predetermined distance, as described above, only momentary connection between the supply contact and the encoding and strobe contacts is established to provide N-key rollover in that, even if one or more key switches are held down, the held key switches will not interfere with the strobing and encoding of data from later actuated key switches. Furthermore, the encoded data from each key switch will automatically strobed into the storage register without any timing circuitry to provide the strobe function.

A modification of the key switch of the present invention is illustrated in FIGS. 7, 8 and 9 and parts thereof similar to parts of the key switch of FIGS. 1, 2 and 3 will be given the same reference numbers with added. The key switch of FIGS. 7, 8 and 9 is similar to the key switch 10 with the exception that the contact chamber is centrally disposed with the plunger positioned therearound and that the contacts are held in a separate support mounted in the body.

The key switch 110 includes a body 112 made of a plastic material and having a generally cylindrical outer side wall 114 extending from a base 116 having eight holes 117 annularly spaced in the center thereof. The open top of the body 112 is sealed by a flexible cap 118 made of a plastic or rubber material and having a thickened edge 119 defining a central opening 120 therein. The cap 1 18 has a skirt 121 with an inwardly extending lip 123 at the end thereof and an inwardly extending rib 125 protruding over the top edge of the side wall 114 of the body 112. The cap 118 is secured to the body 112 in sealing engagement, for instance by ultrasonic welding at lip 123 and along skirt 121 or by providing interlocking structure between the side wall of the body and the skirt; and, the portion of the cap 1 18 extending between the skirt 121 and the edge 119 has a dome-like configuration to define a flexible web 127.

A contact support 129 made of a plastic material is secured to base 116 in any suitable manner, such as by adhesive or ultrasonic welding, and has a generally cylindrical wall 124 with diametrically opposed openings 131 formed in the bottom thereof such that top edges 126 thereof are spaced from the base 116 of the body 112. A relief chamber 128 is formed in the body 112 concentrically around the support 129 and is defined by side wall 114 and an annular, inwardly extending, sloping shoulder 130 aligned with the top edges 126 of the openings 131. A contact chamber 132 is defined internally of contact support 129 and communicates through openings 13] with a well 134 for receiving a pool of electrically conductive liquid 136, such as mercury. the well 134 having an annular piston-head receiving portion defined at its perimeter by an upstanding end wall 138 extending from base 116 to shoulder 130.

A plunger 144 formed of a plastic material has a shaft 146 mounting a key top 148 at the top thereof in any suitable manner, and the shaft 146 has a reduced diameter neck 149 for receiving the thickened edge 119 in sealing engagement such that the shaft of the plunger 144 extends through the opening 120 in the cap 118 and into the body 112. The shaft 146 terminates at a round flange 151 which mounts an annular piston-like head 142 by means of diametrically opposed members 153, and the undersurface of flange 151 is contoured to arcuately taper to a centrally disposed apex aligned with the contact chamber 132. The head 142 of the plunger has a sloping upper surface and is axially movable into the annular portion of the well 134 in sealing engagement with end wall 138 and has an axial length or height less than the axial length or height of openings 131 such that when the head 142 rests on the base 116 communication is established between the contact chamber 132 and the relief chamber 128.

The inner surface of wall 124 of support 129 has a bottom portion 155 which tapers outwardly at 157 to a top portion 159, and eight equally spaced bores 161 are annularly arranged in the bottom portion 155 of the wall with two of the bores 161 each aligned with an opening 131, the support 129 being aligned to index the bores 161 with the holes 117 in the base of the body 112. A supply wire contact 160 extends through one of the bores 161 aligned with one of the openings 131 to a contact end 162 extending through the tapered portion 157 of the wall 124 to be exposed in the contact chamber 132 as it extends along the top portion 159 of wall 124 to a position adjacent the open top edge of the wall. Supply contact 160 has a connector end 164 extending through base 116 for connection with a supply bus, such as 86 in FIG. 6. A strobe wire contact 172 extends through the bore 161 aligned with the other opening 131 and has insulation 173 therearound such that only a small portion of the wire is exposed above the tapered portion of the wall 124 to define a contact end 174 which is arranged substantially centrally between the tapered portion 157 of wall 124 and the open top end of the wall. Strobe contact 172 has a connector end 176 extending through the base 116 of the body 112 for connection with a strobe input of a register, such as via connector 90 in FIG. 6. Six encoding wire contacts 166 extend through the remaining bores 161 to define contact ends 168 extending along the top portion 159 of the wall to positions adjacent the open thereof and connector ends 170 extending through the base 116 of the body for connection with data inputs of a register, such as via connectors 92, 94, 96, 98, 100 and 102 in FIG. 6. The contact ends of the supply, strobe and encoding contacts are arranged in the contact chamber 132 such that the contact ends 162 and 168 of the supply and encoding contacts are exposed below and above the contact end 174 of the strobe contact whereby the mercury 136 will contact the strobe contact after contacting the encoding contacts and will interrupt contact with the strobe contact before interrupting contact with the encoding contacts in order to provide a strobe signal having a leading edge after the leading edges of the encoded data signals and a trailing edge before the trailing edges of the encoded data signals to permit use of the key switches 110 universally with leading edge and trailing edge operated logic circuitry in the electronic equipment.

The operation of the key switch 1 10 will be described with reference to FIGS. 10A, 10B, 10C and 10D wherein it can be seen that initially the pool of mercury 136 is disposed in the body 112 to be received in the well 134 in both the annular outer portion and the central portion extending through the support 129, the top level of the mercury being about level with the top edge 126 of the openings 131 and the shoulder 130, as shown in FIG. 10A. With the key switch in the rest position, the mercury 136 will only make contact with the supply contact 160, the plunger 144 being biased out of the well 134 by the flexible web 127 of the cap 118 such that the head 142 of the plunger is spaced from the pool of mercury 136.

The key switch 110 is actuated by applying pressure to the key top 148 which will overcome the bias of the flexible web of the cap 118 to axially move the plunger 144 into the body 1 12 with the annular piston-like head 142 sealably engaging the end wall 138 of the well 134 to prevent the mercury 136 from escaping into the relief chamber 128 and force the mercury through the openings 131 into the contact chamber 132, as shown in FlG. 108. The mercury being forced up the central contact chamber 132 will have a spherically shaped upper surface and will initially establish electrical connection between the supply contact and the encoding contacts and thereafter will contact the strobe contact to provide a leading edge for the strobe signal after the leading edges of the data input signals.

After the plunger has been axially moved a predetermined distance, such as to move head 142 to abut base 116, the openings 131 will be unblocked clue to the axial height of the head 142 being smaller than the height of the openings 131, and the mercury in the contact chamber 132 will collapse and flow out of the contact chamber through the openings 131 and over the piston head 142 to the relief chamber 128. If the key switch is depressed with sufficient force, the initial velocity imparted to the mercury can cause some of the mercury to exit the contact chamber 132 through the open top of the wall 124 with the contoured undersurface of the flange 151 providing a baffle to deflect the mercury into the relief chamber 128. The arrangement of the strobe and encoding contacts is such that the leading and trailing edges of the strobe signal will be between the leading and trailing edges of the data signals even when the mercury is forced over the top of the wall 124 since the encoding contacts 166 extend above the strobe contact 172.

Upon removal of pressure applied to the key top 148, the bias of the flexible web 127 of the cap 118 will move the lead 142 of the plunger out of the well 134; and, once the head 142 clears the shoulder 130 in the relief chamber, as shown in FIG. 10D, the mercury will return to the well 134 aided by the sloping contour of the shoulder 130 and the upper surface of the head 142. Thus, the key switch will be returned to the rest position, as illustrated in FIG. 10A, in preparation for the next actuation. 7

From the above, it will be appreciated that the operation of the key switch 110 is similar to that described above with respect to the key switch 10 with only the positioning of the contact chamber being altered; and, accordingly, actuation of the key switch 110 establishes only momentary contact to provide N-key rollover and strobe functions while tactile feedbback is provided by the collapsing of the mercury in the Contact chamber once the openings have been unblocked by movement of the plunger a predetermined distance and, to some degree, by the cap 118 as the curvature of the web 127 is reversed.

The relief chamber in the key switches of the present invention facilitates the return stroke of the plunger after the downward stroke by providing a path for the mercury around the piston-like head thereby permitting extremely fast operation, and the relief chamber could have any suitable configuration and could be formed by any suitable structure to provide such function. For instance, the space above the head of the plunger could define at least a portion of the relief chamber. The cooperation of the configuration of the plunger head and the openings communicating with the contact chamber define a path for at least a portion of the mercury from the contact chamber to the relief chamber in accordance with the present invention such that, once the plunger is moved a predetermined distance, mercury in the contact chamber can exit with at least a portion thereof received in the relief chamber to facilitate return to the well on the return stroke of the plunger. The structural components of the key switches according to the present invention are preferably made from a plastic material with as few parts as possible while providing the desired cooperation between the wall structure of the body and the structure of the plunger; however, other suitable materials could be utilized in the construction of the key switches of the present invention.

The supply, encoding and strobe contacts can be arranged in the key switch body in any suitable manner, preferably at different vertical levels, such that the supply contact is spaced from the encoding contacts to be bridged by the mercury and such that the mercury contacts the strobe contact after contacting the encoding contacts. Furthermore, it is advantageous to arrange the strobe contact relative to the encoding contacts such that the mercury disconnects the strobe contact before the encoding contacts such that the key switches can be used with both leading and trailing edge circuitry. The supply contact can be disposed at any position to establish connection with the strobe and encoding contacts upon actuation of the key switch; and, to this end, the supply contact need not contact the mercury when the key switch is in the rest position but only when the mercury enters the contact chamber.

Inasmuch as the present invention is subject to many variations, modifications and changes in detail, it is intended that all matter described above or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.

1. An electrical key switch comprising body means including well means for storing a pool of electrically conductive liquid, contact chamber means communicating with said well means for receiving said liquid from said well means and relief chamber means for receiving said liquid from said contact chamber means and returning said liquid to said well means;

electrical contact means mounted in said body means and extending into said contact chamber means;

plunger means movable into said well means to displace said liquid from said well means into said contact chamber means and movable out of said well means to permit said liquid to flow from said relief chamber means to said well means; and

means for providing a path between said contact chamber means and said relief chamber means to permit direct flow of said liquid from said contact chamber means to said relief chamber means whereby said liquid remains in said contact chamber means momentarily.

2. An electrical key switch as recited in claim 1 wherein said electrical contact means includes a supply contact and a plurality of encoding contacts spaced from said supply contact, said supply contact and said encoding contacts being electrically connected by said liquid in said contact chamber means when said plunger means is moved into said well means.

3. An electrical key switch as recited in-claim 2 wherein said contact chamber means is substantially vertically disposed and has a bottom end for receiving said liquid from said well means, and said electrical contact means includes a strobe contact disposed above said encoding contacts whereby said liquid contacts said strobe contact after said encoding contacts.

4. An electrical key switch as recited in claim 3 wherein said electrically conductive liquid is mercury.

5. An electrical key switch as recited in claim 1 wherein said means for providing a path for said liquid from said contact chamber means to said relief chamber means includes a head for said plunger means and an opening between said well means and said contact chamber means, said head having a configuration to force said liquid from said well means through said opening into said contact chamber means and, after moving a predetermined distance, to unblock said opening to permit said liquid to flow over said head from said contact chamber means to said relief chamber means. 1 r

6. An electrical key switch as recited in claim 1 wherein said well means is defined by a base, said contact chamber means is defined by a wall having at least one opening therein with an edge spaced from said base, and said plunger means includes a head movable to abut said base and having an axial height less than the distance between said edge of said opening and said base to define said means for providing a path to said relief chamber means.

7. An electrical key switch as recited in claim 6 wherein said contact chamber means is substantially vertically disposed, and said electrical contact means includes a supply contact disposed in said contact chamber means, a plurality of encoding contacts spaced from said supply contact and a strobe contact disposed above said encoding contacts, said liquid in said contact chamber means being mercury and electri- :ally connecting said supply contact with said encoding :ontacts prior to electrically connecting said supply :ontact with said strobe contact. 7

8. An electrical key switch as recited in claim 7 wherein said'well means is disposed centrally in said body means and said contact chamber means and said relief chamber means are disposed on opposite sides of said well means.

9. An electrical key switch as recited in claim 7 wherein said contact chamber means is centrally disposed in said body means, said well means has an annular portion extending around said contact chamber means, said relief chamber means extends around said annular portion of said well means, and said head of said plunger means is annular and movable into said annular portion of said well means.

10. An electrical key switch comprising a body having wall means therein defining a well for receiving a pool of mercury and a contact chamber, said wall means having an opening therein for establishing communication between said well and said contact chamber;

contact means disposed in said contact chamber; and

plunger means including a head movable into said well to force said mercury through said opening into said contact chamber to electrically connect said contact means, said head having a configuration such that when said head is moved a predetermined distance into said well, said head will unblock said opening to permit said mercury to exit from said contact chamber whereby electrical connection of saidcontact means is only momentary.

11. An electrical key switch as recited in claim 10 wherein said well is defined by a base, said opening has an edge spaced from said base and said head of said plunger means has a height less than the space between said base and said edge of said opening.

12. An electrical key switch as recited in claim 10 wherein said contact chamber is centrally disposed in said body, said well has an annular portion surrounding said contact chamber, and said head of said plunger means is annular and movable into said annular portion of said well.

.13. An electrical key switch as recited in claim 10 wherein said well is centrally disposed in said body and has a cylindrical configuration, said contact chamber is radially spaced from said well, said head of said plunger means has a cylindrical configuration, and said plunger means includes a shaft connected wtih said head by a portion having a diameter less than the diameter of said head.

14. An electrical key switch as recited in claim 10 and further comprising a cap connecting said body and said plunger means and having a dome-shaped web biasing said head of said plunger means away from said well.

15. An electrical key switch as recited in claim 10 wherein said contact means includes a supply contact, a plurality of encoding contacts spaced from said supply contact an a strobe contact, said supply contact and said encoding contacts being electrically connected by said mercury in said contact chamber when said plunger means is moved into said well before said supply contact and said strobe contact are connected and the connection between the supply contact and the strobe contact being broken before the connection between said supply contact and said encoding contacts is broken. i 7

16. A keyboard system comprising a plurality of key switches each including a body having a pool of mercury therein, a supply contact, a strobe contact, a plurality of encoding contacts, and plunger means depressible for moving said mercury to momentarily establish an electrical connection between said supply contact and said strobe and encoding contacts even with said plunger means remaining depressed;

register means having a plurality of data inputs and a strobe input;

means connecting each of said supply contacts of said key switches with a supply potential;

a plurality of data connector means each connected with one of said data inputs of said register means, predetermined ones of said encoding contacts of each of said key switches being connected with predetermined ones of said key switches being connected with predetermined ones of said connector means; and

strobe connector means connecting each of said strobe contacts of said key switches with said strobe input of said register means whereby actuation of any of said key switches produces coded data signals on said encoding contacts and a strobe signal on said strobe contact to enter said coded data signals into said register means.

17. A keyboard system as recited in claim 16 wherein each of said key switches includes means positioning said strobe contact relative to said encoding contacts such that said supply potential is connected with said strobe contact after being connected with said encoding contacts and said supply potential is disconnected from said strobe contact before being disconnected from said encoding contacts.

18. A keyboard system as recited in claim 16 wherein said body of each of said key switches includes a well receiving said pool of mercury, a contact chamber defined by a wall having an opening therein communicating with said well and a relief chamber for receiving said mercury from said contact chamber, said supply strobe and encoding contacts being disposed in said contact chamber, and said plunger means for moving said mercury includes a head movable into said well to displace said mercury through said opening into said contact chamber, said head having a configuration to unblock said opening after moving a predetermined distance to permit said mercury to flow over said head to said relief chamber.

19. A self-encoding key switch comprising well means for storing a pool of mercury;

contact chamber means extending above said well means and having a supply contact, a strobe contact and plurality of encoding contacts disposed therein, said strobe contact being arranged at a different vertical level than at least a portion of each said encoding contacts; and

plunger means movable into said well means to displace said mercury into said contact chamber to establish momentary electrical connection only between said supply contact and said encoding and strobe contacts even when said plunger means remains in said Well means, said mercury contacting said encoding contacts before contacting said strobe contact whereby the leading edges of data signals from said encoding contacts precede the leading edge of a strobe signal from said strobe contact,

20. A self-encoding key switch as recited in claim 19 wherein said contact chamber has a closed upper end, said strobe contact is disposed above at least a portion of each of said encoding contacts and said plunger means includes means for permitting said mercury in said contact chamber to collapse after momentarily connecting said supply contact with said strobe and encoding contacts whereby the trailing edges of said data signals are produced after the trailing edge of said strobe signal.

21. A selfencoding key switch as recited in claim 19 wherein said contact chamber has an open upper end, and each of said encoding contacts has a portion disposed below said strobe contact and a portion disposed above said strobe contact whereby said mercury breaks contact with said strobe contact before said encoding contacts whether said mercury is moving up or down through said Contact chamber to produce a trailing edge for said strobe signal before the trailing edges of said data signals.

22. A self-encoding key switch as recited in claim 21 wherein said well means includes an annular portion surrounding said contact chamber and said plunger means includes an annular head movable into said annular portion of said well means.

23. A self-encoding key switch as recited in claim 22 wherein said well means is defined by a base, said contact chamber is defined by a cylindrical wall having an open upper end and extending from said base and having openings therein communicating with said annular portion of said well means, said openings having an upper edge spaced from said base, and said head of said plunger means having a height less than the distance between said upper edges of said openings and said base whereby at least a portion of said mercury in said contact chamber collapses when said head is moved past said upper edges of said openings and a portion of said mercury can travel over said open end of said cylindrical wall.

24. A self-encoding key switch as recited in claim 23 and further comprising relief chamber means surrounding said well means for receiving said mercury collapsing in said contact chamber and travelling over said open end of said cylindrical wall.

25. A self-encoding key switch as recited in claim 24 wherein said plunger means includes baffle means aligned with said contact chamber means to deflect said mercury travelling over said open end of said cylindrical wall into said relief chamber means.

26. A self-encoding key switch as recited in claim 25 wherein said well means, contact chamber means, and said relief chamber means are formed in a body having an open top end, and further comprising a flexible cap closing said open top end of said body and connected with said plunger means, said cap having a domeshaped web biasing said head of said plunger means away from said well means.

27. An electrical key switch comprising well means for storing a pool of electrically conduc tive liquid;

wall means mounting electrical contact means;

plunger means movable into said well means to force said liquid along said wall means to electrically connect said contact means; and

passage means including an opening in said plunger means providing a path for said liquid to immediately return to said well means from said wall for receiving said liquid from said opening in said plunger means and storing said liquid until said plunger means has been withdrawn from said well means.

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1. An electrical key switch comprising body means including well means for storing a pool of electrically conductive liquid, contact chamber means communicating with said well means for receiving said liquid from said well means and relief chamber means for receiving said liquid from said contact chamber means and returning said liquid to said well means; electrical contact means mounted in said body means and extending into said contact chamber means; plunger means movable into said well means to displace said liquid from said well means into said contact chamber means and movable out of said well means to permit said liquid to flow from said relief chamber means to said well means; and means for providing a path between said contact chamber means and said relief chamber means to permit direct flow of said liquid from said contact chamber means to said relief chamber means whereby said liquid remains in said contact chamber means momentarily.
 2. An electrical key switch as recited in claim 1 wherein said electrical contact means includes a supply contact and a plurality of encoding contacts spaced from said supply contact, said supply contact and said encoding contacts being electrically connected by said liquid in said contact chamber means when said plunger means is moved into said well means.
 3. An electrical key switch as recited in claim 2 wherein said contact chamber means is substantially vertically disposed and has a bottom end for receiving said liquid from said well means, and said electrical contact means includes a strobe contact disposed above said encoding contacts whereby said liquid contacts said strobe contact after said encoding contacts.
 4. An electrical key switch as recited in claim 3 wherein said electrically conductive liquid is mercury.
 5. An electrical key switch as recited in claim 1 wherein said means for providing a path for said liquid from said contact chamber means to said relief chamber means includes a head for said plunger means and an opening between said well means and said contact chamber means, said head having a configuration to force said liquid from said well means through said opening into said contact chamber means and, after moving a predetermined distance, to unblock said opening to permit said liquid to flow over said head from said contact chamber means to said relief chamber means.
 6. An electrical key switch as recited in claim 1 wherein said well means is defined by a base, said contact chamber means is defined by a wall having at least one opening therein with an edge spaced from said base, and said plunger means includes a head movable to abut said base and having an axial height less than the distance between said edge of said opening and said base to define said means for providing a path to said relief chamber means.
 7. An electrical key switch as recited in claim 6 wherein said contact chamber means is substantially vertically disposed, and said electrical contact means includes a supply contact disposed in said contact chamber means, a plurality of encoding contacts spaced from said supply contact and a strobe contact disposed above said encoding contacts, said liquid in said contact chamber means being mercury and electrically connecting said supply contact with said encoding contacts prior to electrically connecting said supply contact with said strobe contact.
 8. An electrical key switch as recited in claim 7 wherein said well means is disposed centrally in said body means and said contact chamber means and said relief chamber means are disposed on opposite sides of said well means.
 9. An electrical key switch as recited in claim 7 wherein said contact chamber means is centrally disposed in said body means, said well means has an annular portion extending around said contact chamber means, said relief chamber means extends around said annular portion of said well means, and said head of said plunger means is annular and movable into said annular portion of said well means.
 10. An electrical key switch comprising a body having wall means therein defining a well for receiving a pool of mercury and a contact chamber, said wall means having an opening therein for establishing communication between said well and said contact chamber; contact means disposed in said contact chamber; and plunger means including a head movable into said well to force said mercury through said opening into said contact chamber to electrically connect said contact means, said head having a configuration such that when said head is moved a predetermined distance into said well, said head will unblock said opening to permit said mercury to exit from said contact chamber whereby electrical connection of said contact means is only momentary.
 11. An electrical key switch as recited in claim 10 wherein said well is defined by a base, said opening has an edge spaced from said base and said head of said plunger means has a height less than the space between said base and said edge of said opening.
 12. An electrical key switch as recited in claim 10 wherein said contact chamber is centrally disposed in said body, said well has an annular portion surrounding said contact chamber, and said head of said plunger means is annular and movable into said annular portion of said well.
 13. An electrical key switch as recited in claim 10 wherein said well is centrally disposed in said body and has a cylindrical configuration, said contact chamber is radially spaced from said well, said head of said plunger means has a cylindrical configuration, and said plunger means includes a shaft connected wtih said head by a portion having a diameter less than the diameter of said head.
 14. An electrical key switch as recited in claim 10 and further comprising a cap connecting said body and said plunger means and having a dome-shaped web biasing said head of said plunger means away from said well.
 15. An electrical key switch as recited in claim 10 wherein said contact means includes a supply contact, a plurality of encoding contacts spaced from said supply contact an a strobe contact, said supply contact and said encoding contacts being electrically connected by said mercury in said contact chamber when said plunger means is moved into said well before said supply contact and said strobe contact are connected and the connection between the supply contact and the strobe contact being broken before the connection between said supply contact and said encoding contacts is broken.
 16. A keyboard system comprising a plurality of key switches each including a body having a pool of mercury therein, a supply contact, a strobe contact, a plurality of encoding contacts, and plunger means depressible for moving said mercury to momentarily establish an electrical connection between said supply contact and said strobe and encoding contacts even with said plunger means remaining depressed; register means having a plurality of data inputs and a strobe input; means connecting each of said supply contacts of said key switches with a supply potential; a plurality of data connector means each connected with one of said data inputs of said register means, predetermined ones of said encoding contacts of each of said key switches being connected with predetermined ones of said key switches being connected with predetermined ones of said connector means; and strobe connector means connecting each of said strobe contacts of said key switches with said strobe input of said register means whereby actuation of any of said key switches produces coded data signals on said encoding contacts and a strobe signal on said strobe contact to enter said coded data signals into said register means.
 17. A keyboard system as recited in claim 16 wherein each of said key switches includes means positioning said strobe contact relative to said encoding contacts such that said supply potential is connected with said strobe contact after being connected with said encoding contacts and said supply potential is disconnected from said strobe contact before being disconnected from said encoding contacts.
 18. A keyboard system as recited in claim 16 wherein said body of each of said key switches includes a well receiving said pool of mercury, a contact chamber defined by a wall having an opening therein communicating with said well and a relief chamber for receiving said mercury from said contact chamber, said supply strobe and encoding contacts being disposed in said contact chamber, and said plunger means for moving said mercury includes a head movable into said well to displace said mercury through said opening into said contact chamber, said head having a configuration to unblock said opening after moving a predetermined distance to permit said mercury to flow over said head to said relief chamber.
 19. A self-encoding key switch comprising well means for storing a pool of mercury; contact chamber means extending above said well means and having a supply contact, a strobe contact and plurality of encoding contacts disposed therein, said strobe contact being arranged at a different vertical level than at least a portion of each said encoding contacts; and plunger means movable into said well means to displace said mercury into said contact chamber to establish momentary electrical connection only between said supply contact and said encoding and strobe contacts even when said plunger means remains in said well means, said mercury contacting said encoding contacts before contacting said strobe contact whereby the leading edges of data signals from said encoding contacts precede the leading edge of a strobe signal from said strobe contact.
 20. A self-encoding key switch as recited in claim 19 wherein said contact chamber has a closed upper end, said strobe contact is disposed above at least a portion of each of said encoding contacts and said plunger means includes means for permitting said mercury in said contact chamber to collapse after momentarily connecting said supply contact with said strobe and encoding contacts whereby the trailing edges of said data signals are produced after the trailing edge of said strobe signal.
 21. A self-encoding key switch as recited in claim 19 wherein said contact chamber has an open upper end, and each of said encoding contacts has a portion disposed below said strobe contact and a portion disposed above said strobe contact whereby said mercury breaks contact with said strobe contact before said encoding contacts whether said mercury is moving up or down through said contact chamber to produce a trailing edge for said strobe signal before the trailing edges of said data signals.
 22. A self-encoding key switch as recited in claim 21 wherein said well means includes an annular portion surrounding said contact chamber and said plunger means includes an annular head movable into said annular portion of said well means.
 23. A self-encoding key switch as recited in claim 22 wherein said well means is defined by a base, said contact chamber is defined by a cylindrical wall having an open upper end and extending from said base and having openings therein communicating with said annular portion of said well means, said openings having an upper edge spaced from said base, and said head of said plunger means having a height less than the distance between said upper edges of said openings and said base whereby at least a portion of said mercury in said contact chamber collapses when said head is moved past said upper edges of said openings and a portion of said mercury can travel over said open end of said cylindrical wall.
 24. A self-encoding key switch as recited in claim 23 and further comprising relief chamber means surrounding said well means for receiving said mercury collapsing in said contact chamber and travelling over said open end of said cylindrical wall.
 25. A self-encodiNg key switch as recited in claim 24 wherein said plunger means includes baffle means aligned with said contact chamber means to deflect said mercury travelling over said open end of said cylindrical wall into said relief chamber means.
 26. A self-encoding key switch as recited in claim 25 wherein said well means, contact chamber means, and said relief chamber means are formed in a body having an open top end, and further comprising a flexible cap closing said open top end of said body and connected with said plunger means, said cap having a dome-shaped web biasing said head of said plunger means away from said well means.
 27. An electrical key switch comprising well means for storing a pool of electrically conductive liquid; wall means mounting electrical contact means; plunger means movable into said well means to force said liquid along said wall means to electrically connect said contact means; and passage means including an opening in said plunger means providing a path for said liquid to immediately return to said well means from said wall means whereby said liquid connects said contact means only momentarily.
 28. An electrical key switch as recited in claim 27 wherein said passage means includes a relief chamber for receiving said liquid from said opening in said plunger means and storing said liquid until said plunger means has been withdrawn from said well means. 